This invention relates to a method and apparatus for controlling the speed of travelling of an automotive vehicle and, more particularly, to a vehicle speed control method and apparatus for maintaining the vehicle speed at a demand value when an operator's demand occurs.
As well known in the art, vehicle speed automatic control apparatus include a control circuit which provides a feedback control signal containing integral plus proportional terms generated in response to the sensed deviation of the vehicle travelling speed from a demand speed. This feedback control signal is utilized by a throttle valve actuator to adjust the throttle valve position in a sense and direction to correct the vehicle speed deviation.
In order to improve the control characteristic of the vehicle speed automatic control apparatus, it is required to increase the speed of response to occurrence of a deviation between the demand and actual vehicle speeds and also to minimize the tendency toward hunting which results in repeated deviation of the vehicle travelling speed from the demand value in a short time. It is understood, of course, that the control characteristic is greatly dependent on the vehicle running characteristic which differs from one vehicle type to another.
In recent years, many of such vehicle speed control apparatus employ a large scale integrated circuit (LSI circuit) forming therein a digital computer for calculating the value of the control signal applied to the throttle valve actuator. In order to produce such large scale integrated circuits on a mass production basis at remarkably low cost, it is particularly desirable that they are applicable for various types of vehicle. However, the large scale integrated circuits should be produced to match with respective vehicle running characteristics which differ from one vehicle type to another. For the same type of vehicle, the running characteristic is affected by changes in various factors including engine performance, running resistance, transmission loss, and transmission gear ratio. The engine performance changes with the lapse of time. The running resistance changes with changes in loaded weight and tire air pressure.
Therefore, it is the problem in the art to provide a vehicle speed control apparatus applicable commonly in various types of vehicle without any degradation in control stability and response speed.